Conventional automatic type firearms, particularly air-cooled automatic firearms, have a serious operational limitation in that the firearm barrel can easily overheat when firing long continuous bursts of ammunition. Thus, after a period of continuous use, a firearm such as a machine gun must be taken out of operation unless long, continuous bursts have been avoided. Otherwise, malfunction or permanent damage to the firearm may result. Various remedies have been proposed to overcome the overheating problem in such firearms, the most satisfactory remedy being simply to exchange the overheated barrel for another barrel which is at ambient or reduced temperature.
While this practice of exchanging barrels tends to eliminate the overheating problem of automatic firearms, it introduces an additional operational limitation in terms of the time required to change barrels which, of course, renders the firearm inoperative during the period of time in which changing of the barrels is effected. Thus, the hot barrel of the firearm should be easily detachable and the new barrel should be quickly attachable. Moreover, the barrel must be able to provide the proper headspacing of the firearm due to the accumulation of manufacturing tolerances which affect the headspace. Variations in headspace cause the distance from the head of a cartridge seated in the chamber of the barrel to the bolt to vary to such a degree that, on one hand, the bolt may not be closed on a cartridge and thus the firearm cannot be fired, and on the other, the face of the bolt does not support the head of the cartridge and as a consequence the cartridge case may rupture when fired.
Barrels of the exchangeable type for use with automatic firearms and the like have utilized an interrupted type of thread, that is, several portions of the threads on one end of the barrel and in the breech are interrupted to allow an axial sliding assembly of the two components and then allow a small rotational movement to lock them together. The thread interruptions are usually spaced about the barrel and breech, three interruptions being the most common spacing arrangement.
As an improvement in this art, it is an object of the present invention to provide an exchangeable barrel and barrel mounting or extension, which allows the mounting and barrel to be joined and separated quickly and easily, and in which joinder is effected consistently and to the same position every time. Expressed otherwise, it is a feature of this invention to provide a barrel and mounting which, as joined, will form a headspace that will not vary on each assembly of the barrel on the mounting and will remain constant despite repeated firing of the weapon.
It is another object of the present invention to provide a barrel and mounting which cooperate in such a manner that the barrel is maintained against accidental changes in headspace of the firearm, such as by further rotation of the barrel to move the barrel axially toward or away from the barrel mounting.